1. Field of the Invention
This invention relates to a process to change the relative positions of a plurality of elements aligned in a first configuration so as to place them, on line, in a second configuration. The invention also relates to a device for using this process. In particular, the invention relates to a process and device to automatically change the relative positions of injectors (also called feed tubes) for pulverulent products in suspension in a gas, in which the injectors are held in a distribution nozzle and spray the pulverulent product on an advancing subjacent support in order to obtain on this support a film with particular properties.
2. Background of the Related Art
It is known, particularly from patent FR 2 427 141 and European patent application A-125 153, to continuously distribute on an advancing substrate, such as a ribbon of glass, pulverulent products in suspension in a gas, through a distribution slot placed above the substrate and extending crosswise to the direction of movement of the latter. This slot comprises the lower end of a distribution device also called a nozzle, which has a cavity extending over the entire length of the slot. This cavity is fed with pulverulent products in suspension in a gas by a series of injectors aligned parallel to the slot, i.e., crosswise to the direction of movement.
The processes and devices described in these patents serve to form on a substrate, for example on a ribbon of glass, a thin layer having particular properties, particularly optical or electrical properties. To obtain appropriate constant properties over the entire surface of the substrate, it is necessary that the layer not exhibit variations in thickness, or else only very slight such variations.
Despite mixing by creating turbulences in the gas carrying the pulverulent product, despite the introduction of additional gas in the nozzle to regulate the distribution of pulverulent product in time and in space, it has been observed that vertically below each of the injectors of pulverulent product there is formed a deposit, called a trace, of a certain width and whose thickness is non-constant over this width, the maximum thickness being located approximately on the axis of the injector. All of these traces, due to their at least partial overlapping, form the layer deposited on the substrate. When all the injectors fed with pulverulent product are suitably spaced, the overlapping of the traces of each injector leads to a homogeneous deposit. When the deposit is not homogeneous, as a result of too great or too little a thickness in a given area, the distance between the injectors is changed, which has the effect of changing the overlapping of the traces. Thus, when the coating is too thick in an area, the injectors are separated, and when the thickness is insufficient, the distance is reduced between the injectors to obtain, over the entire substrate, a uniform thickness.
The uniformity of the coating, and consequently that of its thickness, is determined by measuring the variations in the reflection of the light by the coating, by using an apparatus called a spotmeter. This measurement of the reflection makes it possible to determine the thickness value governed initially by the regulation of the flow of the pulverulent product. If the measurement indicates that the thickness is not suitable, the arrival of pulverulent product is then cut off to permit changing the distances between the injectors as a function of the observed defect, i.e., as has already been described, by moving the injectors apart or by bringing them closer together, depending on whether the thickness is too great or too small.
This process has many drawbacks. For example, the reflection measurements take place off the production line on a crosswise strip of glass 100 mm wide. These measurements, therefore, can be performed only after a certain time after the appearance of the defects in the coating. In addition, corrections based upon these measurements require additional time, with the result that about 30 min. elapse between the production of the glass that is being controlled and the control operation.
Since up to 30 min. are required to adjust distances between the injectors, and since the speed of advance of the ribbon of glass can vary between 6 and 25 m/min, it can be appreciated that the production loss which can result, and which corresponds not only to the amount of glass treated before the optical measurement but also to the glass surface which could have been produced during the period of adjusting the distances between injectors, is quite high. The production capacity is thus limited.
Therefore, it is necessary to find a system making possible a quick adjustment of the distances between the injectors as soon as the defects have been determined by the optical measurement.